The present invention relates to fuel injection system and an ignition system for engine control, and more particularly to methods of measuring the variables indicative of the state of an engine and controlling an engine on the basis of the measured results, which is well suited to reliably perform control of the engine for all engine speeds by means of a computer for governing the principal functions of the above systems.
As described in "SYSTEMS AND CONTROL," Vol. 24, No. 5, pp. 306-312, 1980 (Japanese language) the individual operations of a computer program in a prior-art engine control system are of two; one started at time intervals and the other started in accordance with engine crank revolution angles.
The prior art employed the measurement and control of the variables of an engine state started at two timings of a time interval and a crank angle (abbreviated to "CA") position, and has had the problem of mismatching attendant upon the different kinds of timings. When the measurement of the revolution number of the engine and the utilization thereof are mentioned as an example, the revolution number is measured by counting crank angle pulses (for example, 360 pulses/revolution) at certain time intervals, and the counted value is input to a computer every 10 ms. However, this counted value is not synchronous with the crank angle position of the engine. In case of performing a macro-control with average values of data in the equilibrium state in which the engine revolution number hardly changes, even the data asynchronous to the crank angle position is valid. However, in case of finely controlling the revolution number which is the integrated result of nonlinear torques generated by explosion, disadvantageously the data asynchronous to the crank angle position does not correspond to the explosion phenomena.
In U.S. Pat. No. 3,969,614 (Ford Motor Co.), controlled variables are calculated in accordance with electric signals expressive of a selected instant in time while the engine is operative as understood from the statements of column 2, lines 5-9, and column 2, line 26-45 as cited below, but this patent does not define the timing of the calculation.
Statements of column 2, line 5-9: "A main object of the invention is to employ a digital computer to calculate, on a real-time basis, that is, while the engine is operative, proper settings for one or more of the controlled variables from measurements made on one or more variable engine conditions."
Statements of column 2, line 26-45: "While the engine is operative, an electrical signal is generated in the form of a binary number. This electrical signal is indicative of a condition of the engine as of a selected instant in time. From this binary-number electrical signal indicative of a condition of the engine, a digital computer arithmetically calculates a value corresponding to a setting of the means for controlling the energy conversion process. The digital computer is programmed to calculate the control value from an algebraic function or functions describing a desired relationship between the sensed engine condition and settings of the means for controlling the energy conversion process. The resulting value, in the form of a binary number, is converted into a setting of the means for controlling the energy conversion process. The conversion of the binary number into a setting of the engine controlling means is accomplished with the aid of a suitable electrical circuit coupled between the digital computer and the engine controlling means."
The variables which are sensed for the setting calculations and the controlled variables which are output as calculated results, are defined in the statement of column 1, lines 50-67, "The controlled variables are throttle angle, which controls the amounts of air supplied to the engine, fuel flow per cycle, fuel-injection timing, ignition timing, and, if EGR is used, the settings of the means used to control the amount of exhaust gases recirculated through the engine. To effect control of these variables that determine the characteristics of the energy conversion process, various engine conditions may be sensed while the engine is operative. Thus one or more of the following variable engine conditions may be sensed: crankshaft position, engine speed, mass air-flow into the engine, intake-manifold pressure, throttle angle, EGR-valve position, throttle-angle rate of change, engine-speed rate of change, fuel temperature, fuel pressure, EGR-valve rate of change, vehicle speed and acceleration, engine coolant temperature, engine torque, air-to-fuel ratio, exhaust emissions, etc." In the specification of the patent, however, no statement is provided as to the timings during the engine operation at which the variables to be sensed for controlling the energy conversion process are measured.
Heretofore, the discussion of the energy conversion process of an engine has been premised on fuel supply by a carburettor. With the carburettor type system, a mixture consisting of fuel and air has been supplied in an amount required by a cylinder. The mixture ratio has been predetermined and maintained despite the volume and speed of the inlet air flow. Also, in a fuel injection system, it has been considered that fuel in a volume corresponding to an inlet air flow may be injected. For such reasons, it can be said that almost no engineer has paid attention to the timing of the measurement of the inlet air flow.
This will be studied from the viewpoint of engine characteristics. A conventional engine is typically heavy in weight and has further been furnished with a flywheel to attain smooth operation. That is, it has had the property of absorbing small disturbances and continuing a stable movement owing to a great moment of inertia. In a recent design, however, the engine has been lightened to provide a high revolution speed and a high response. Due to the high response, the engine is sensitive even to slight disturbances, with the result that fluctuation of the engine revolution, vibration of the car body, etc. are likely to occur.
Further, the aforementioned patent aims at establishing an equilibrium state of the engine operation at all times as understood from the statement of column 2, lines 15-19, "A very important feature of the invention is that it now is possible to eliminate the engine operating instabilities characteristic of prior art engine control systems and, by this elimination, to obtain equilibrium conditions of engine operation at all times." This aim is proper for a conventional engine having a great moment of inertia. For establishing the equilibrium state of such an engine, it has not always been necessary to measure the volume of air and the volume of fuel pertinent to combustion in each cylinder and exhaust gas as a product of the combustion, in synchronism with the timing of the combustion thereof.
As regards the recent engine of light weight and high response, however, it is important for proper engine control to prevent vibrations from occurring or increasing. To this end, individual combustion strokes need to be controlled on the basis that the movement of the engine is a continuation of transient states. For the prevention of the vibrations, the volume of inlet air must be measured in a timely manner and accurately so as to properly set the fuel volume and ignition timing as desired.